A silicon carbide semiconductor device is a semiconductor device which includes a silicon carbide layer, and has excellent technical features such as a high breakdown voltage, low loss, a low leakage current, high-temperature operability, and high-speed operability. Accordingly, the application of the silicon carbide semiconductor device to a power element such as a switching element or a rectifying element has been highly anticipated. As the power element, although a power MOSFET, an IGBT, a Schottky diode, a pn diode, a thyristor or the like has been known, all these power elements have an ohmic electrode which is in contact with a silicon carbide layer so that, in many cases, an electric current of several amperes flows between the silicon carbide layer and the ohmic electrode.
Conventionally, as a method for manufacturing a silicon carbide semiconductor device, there has been known a method described in patent literature 1 (a conventional method for manufacturing a silicon carbide semiconductor device). FIG. 10 is a view for explaining the conventional method for manufacturing a silicon carbide semiconductor device. FIG. 10(a) to FIG. 10(e) are views showing respective steps.
The conventional method for manufacturing a silicon carbide semiconductor device sequentially includes, as shown in FIG. 10, a conductive layer forming step where a conductive layer 922 made of nickel is formed on a silicon carbide layer 910 (see FIG. 10(a)), a heat treatment step where the silicon carbide layer 910 and the conductive layer 922 are made to react with each other thus forming an alloy layer formed of a reaction layer 920 which is in contact with the silicon carbide layer 910 and a silicide layer 924 present on the reaction layer 920 (see FIG. 10(b) and FIG. 10(c)), an etching step where at least a portion of the silicide layer 924 is removed using an acid thus exposing at least a portion of a surface of the reaction layer 920 (see FIG. 10(d)), and an electrode layer forming step where one electrode layer 940 and the other electrode layers 942 are formed on the exposed surface of the reaction layer 920 (see FIG. 10(e)) in this order.
According to the conventional method for manufacturing a silicon carbide semiconductor device, the alloy layer formed of the reaction layer 920 and the silicide layer 924 is formed on the surface of the silicon carbide layer 910 and, thereafter, the surface of the reaction layer 920 is exposed, and the electrode layer 940 and another electrode layer 942 are formed on the exposed surface of the reaction layer 920. Accordingly, not only the electrode layer 940 and the silicon carbide layer 910 are favorably bonded to each other with the reaction layer 920 interposed therebetween but also it is possible to eliminate a possibility that a carbon component in the silicon carbide layer 910 diffuses into the electrode layer 940. As a result, the concentration of carbon in the surface of the electrode layer 940 can be lowered and hence, the adhesiveness between the electrode layer 940 and the other electrode layer 942 formed on the electrode layer 940 can be improved. Accordingly, it is possible to provide a highly reliable silicon carbide semiconductor device 900 where a possibility that the delamination of an electrode can be suppressed while ensuring a favorable contact between the silicon carbide layer and the electrode layer.